This chapter provides an overview of what anxiety problems are, and why the perinatal period features all the key ingredients that can lead to problemmatic anxiety. Nurturing and caring for a baby is not easy for anyone and involves large emotional and physical demands, managing uncertainty and avoiding harm. All in the context of disturbed sleep and a major life change. The cognitive-behavioural model of anxiety states that it is not just the situation we find ourselves in, but the particular meaning we give to our experiences that drive and make sense of our emotions and other responses. In pregnancy and the postnatal period these meanings may be influenced by a complicated and sometimes traumatic journey to pregnancy and birth, beliefs about the importance of thoughts or physical sensations, and how we respond to the responsibility of being pregnant or in charge of a baby, as well as other personal and historical factors. There are many common factors across anxiety problems. In the rest of the book we explain how to apply this basic understanding to overcome particular forms of maternal anxiety.